Method of controlling a vtg engine

ABSTRACT

When controlling an engine having a Variable Turbine Geometry (VTG) the VTG is closed some predicted time period before an up-gear shift is performed. This is advantageous because when the gear shift begins the engine breaking is already maximized and full engine brake can be obtained during the entire gear shift operation.

TECHNICAL FIELD

The present invention relates to a method and a system for controlling acombustion engine for propelling a motor vehicle. In particular thepresent invention relates to a method and apparatus for controlling amotor vehicle equipped with an engine employing Variable TurbineGeometry (VTG) Technology.

BACKGROUND

An engine used in trucks can be provided with a Variable TurbineGeometry (VTG) also termed Variable Geometry Turbocharger or VariableGeometry Turbine (VGT). One reason for employing VTG technology is thatit facilitates fulfillment of emission requirements for i.a. dieselengines.

As is the case for all gear shifting there is a desire to minimize thetime required to carry out the gear shift. This is because during gearshift there should not be any torque on the drive line. Gear shifting isalso described in the international patent application having theinternational publication number WO 03/018974. Furthermore, in the U.S.Pat. No. 6,089,018 a method of controlling a VTG during gear shift isdescribed.

Hence, there exist a need for a method and a system that is capable ofproviding a quick gear shift.

SUMMARY

It is an object of the present invention to provide a method and asystem that is capable providing a quick gear shift.

It is another object of the present invention to provide a method and asystem that is capable of providing a quick retardation of the enginespeed during gear shift.

These objects and others are obtained by the method, system and computerprogram product as set out in the appended claims. Thus, closing the VTGto a maximally acceptable closed position and keeping the VTG in such aposition during the gear shift will allow a quick retardation of theengine speed.

In order to obtain a quick deceleration of the engine speed whenup-shifting, the VTG can be set to act as an engine braking device.Hence, by creating a high exhaust gas pressure upstream the VTG turbinethat pressure will increase the pumping losses of the engine hencestriving to decelerate the engine speed. In such an operation the moreclosed the VTG, the more pump losses will have to be overcome by theengine and as a result the engine speed will decelerate quicker.However, the VTG can only sustain a certain pressure drop. Hence, thepressure difference over the VTG can not be allowed to exceed aninherent value particular to each type of VTG.

Knowing the maximally allowed pressure difference over the VTG andcontrolling the VTG to be as closed as possible without exceeding themaximally allowed pressure, the VTG will act to decelerate the enginespeed as quickly as possible without endangering the VTG. The result ofsuch a control strategy is a very fast deceleration of the engine speedand as a consequence the gear shift can be made quicker.

In one embodiment the VTG is closed some time period before a gear shiftis performed based on a prediction of a future up-gear shift. This isadvantageous because when the gear shift begins the engine breaking isalready maximized and full engine brake can be obtained during theentire gear shift operation.

In one embodiment maximal VTG breaking is obtained by controlling theexhaust gas pressure to a maximally allowed pressure value withoutendangering the Variable Turbine Geometry. This is advantageous becauseit allows for a robust control of the VTG that does not depend on amodel. This may be advantageous in some circumstances.

In one embodiment, the control system is adapted to determining theeffective flow area for the Variable Turbine Geometry, and todetermining the maximally allowed closed position for the VariableTurbine Geometry from the determined effective flow area of the VariableTurbine Geometry. Hereby a fast calculation of the optimal VTG positioncan be obtained whereby the control method can be made fast andaccurate.

In one embodiment the control system has access to a stored map ofVariable Turbine Geometry positions for different effective flow areaswhereby the maximally closed Variable Turbine Geometry position directlycan be determined to be the position corresponding to the effective flowarea of the map, which even further speeds up the time required forfinding the optimal VTG position.

In one embodiment the control system is adapted to repeatedly update themaximally allowed closed position for the Variable Turbine Geometryduring the gear shift. Hereby it is assured that the optimal closedposition is applied for the entire time period when gear shift is inprogress. Also it is ensured that the VTG is closed to a position wherethe VTG is not endangered.

In another embodiment the engine breaking properties of a VTG arecombined with a conventional exhaust gas engine breaking device, such asan exhaust break located downstream the turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way ofnon-limiting examples and with reference to the accompanying drawings,in which:

FIG. 1 a is a general partial view of a drive line comprising an engineincluding a turbo charger with VTG,

FIG. 1 b is a view illustrating the exhaust gas flow of the engine inFIG. 1 a in more detail,

FIG. 2 is a flowchart illustrating steps performed when controlling anengine with VTG used for propelling a motor vehicle in accordance with afirst embodiment, and

FIG. 3 is a flowchart illustrating steps performed when controlling anengine VTG used for propelling a motor vehicle in accordance with asecond embodiment.

DETAILED DESCRIPTION

In FIG. 1 selected parts of a drive line 100 of a motor vehicle 10 areschematically depicted. The drive line depicted in FIG. 1 can forexample be designed to be part of a truck or any other heavy vehiclesuch as a bus or the like. The drive line 100 comprises an engine 101,e.g. in the form of a diesel engine. The engine 101 comprises aturbocharger driven by a turbine having a Variable Turbine Geometry VTG103. The engine is further connected to a gear box, for example agearbox adapted for automatic gear shifting, 105. The vehicle 10 canalso be provided with an exhaust break as is shown in FIG. 1 b . . . .

The engine 101 and the gearbox 105 are controlled by at least onecontrol unit 107, such as an electronic control unit (ECU). The controlunit is adapted to receive sensor signals from different parts of thevehicle, including, but not limited to, signals used for controlling thegearbox and the engine. The control unit 107 is also adapted to providecontrol signals to different parts and components of the vehicle such asfor example the engine and the gear box.

The control of the different parts and components of the vehicle isgoverned by pre-programmed instructions stored in the control unit. Thepre-programmed instructions typically are in the form of a computerprogram executed by the control unit. By changing the instructions thevehicle can be made to behave differently in a particular situation.Typically, the programmed computer instructions are provided in the formof a computer program product stored 110 on a readable digital storagemedium 108, such as memory card, a Read Only Memory (ROM) a RandomAccess Memory (RAM), an EPROM, an EEPROM or a flash memory.

In FIG. 1 b the exhaust gas flow of the engine depicted in FIG. 1 a isshown in more detail, where the arrows indicate the exhaust gas flowdirection. Thus, downstream the engine the VTG 103 is located. Upstreamthe VTG, e.g. at the beginning of the exhaust gas system, a firstpressure sensor 115 is located. A second pressure sensor 116 is locateddownstream the VTG 103. In addition there may be an exhaust gas break117 provided further downstream the second pressure sensor 116.

In FIG. 2, a flowchart illustrating some procedural steps performed whencontrolling an engine with VTG of a motor vehicle in accordance with oneembodiment of the present invention is shown. Thus, in a first step 201,the control unit calculates the maximally allowed closed position forthe VTG using the current readings from the pressure sensors before andafter the VTG.

The pressure downstream the turbine can also be approximated with theoutside pressure or, for example, using the model below for the pressuredrop in the exhaust system.

$p_{at} = {\frac{p_{{at}\; m}}{2} + \sqrt{\frac{p_{{at}\; m}^{2}}{4} + {K_{res}{RT}_{em}{\overset{.}{m}}_{t}^{2}}}}$

The closed VTG position can for example be calculated using thefollowing prediction calculations:

$\begin{matrix}{{{\overset{.}{m}}_{t} = {A_{t}\frac{p_{bt}}{\sqrt{T_{em}R}}{\Psi \left( {\frac{p_{at}}{p_{bt}},\gamma_{e}} \right)}}}{where}{A_{t} = {A_{r}*C_{d}}}{\gamma_{e} = {c_{p}/c_{v}}}} & (1) \\{{\Psi \left( {\frac{p_{at}}{p_{bt}},\gamma_{e}} \right)} = \left\{ \begin{matrix}\sqrt{\frac{2\; \gamma_{e}}{\gamma_{e}}\begin{pmatrix}{\left( \frac{p_{at}}{p_{bt}} \right)^{\frac{2}{\gamma_{e}}} -} \\\left( \frac{p_{at}}{p_{bt}} \right)^{\frac{\gamma_{e} + 1}{\gamma_{e}}}\end{pmatrix}} & {{{if}\mspace{14mu} \frac{p_{at}}{p_{bt}}} \geq \left( \frac{2}{\gamma_{e} + 1} \right)^{\frac{\gamma_{e}}{\gamma_{e} - 1}}} \\\sqrt{{\gamma_{e}\left( \frac{2}{\gamma_{e} + 1} \right)}^{\frac{\gamma_{e} + 1}{\gamma_{e} - 1}}} & {else}\end{matrix} \right.} & (2)\end{matrix}$

Solving equation (1) for A_(t) gives A_(t) as a function of thefollowing variables.

A _(t) =f({dot over (m)} _(t) ,T _(em) ,p _(bt) ,p _(at))  (3)

Using reference values for the pressure values, and measured values formass flow and exhaust gas temperature, equation (3) gives the effectiveflow area for the VTG that corresponds to the desired pressure drop overthe turbine. Since the effective flow area is a function of VTGposition, VTG positions that correspond to a certain effective flow areaare stored in a map (f2) in the ECU.

VTG Position=f ₂(A _(t))

Description of Variables

{dot over (m)}_(t)=massflow through turbineA_(t)=effective flow area turbineA_(r)=Cross sectional area of flow pathC_(d)=Flow coefficientK_(res)=Tunable model parameterT_(em)=temperature of exhaust gasp_(atm)=atmospheric pressurep_(at)=pressure after turbinep_(bt)=pressure before turbinec_(p)=Specific heat capacity at const. pressurec_(v)=Specific heat capacity at const. volumeR=Ideal gas const.

The calculations performed in step 201 are continuously renewed so thatthe control unit at all times has access to an updated prediction valuefor the closed VTG position. When a gear shift is to be performed andthe present gear is disengaged it is desired to quickly reduce theengine speed to a speed synchronized with the next gear after which thenext gear can be engaged. A high exhaust gas pressure will contribute toreduce the engine speed quicker and hence reduce the time necessary towait before the next gear can be engaged. Therefore it is beneficial toapply a high exhaust gas pressure when a gear shift is to take place.

Thus, when a gear shift is initiated in a second step 203 this event issignaled to the control unit. The signal can for example be a triggersignal from another control unit controlling the gear box, which uponinitiating a gear shift also signals to the control unit controlling theVTG position. The control unit has access to data relating to thecurrently maximum closed VTG position and can emit a control signalsetting the VTG to the corresponding position thereby maximizing theexhaust gas pressure in a third step 205. Thereupon, the procedurechecks if the gear shift has been completed in a fourth step 207. If thegear shift has been completed the procedure ends in a fifth step 209 andthe control of the VTG is performed according to whatever controlstrategy the control unit is programmed to execute.

If, on the other hand, the gear shift has not been completed in step207, the procedure continues to a sixth step 211, where the VTGcalculations as described above are updated so that the VTG can continueto be controlled to the maximum closed position. The procedure thenreturns to step 205 where the VTG is again set to a positioncorresponding to the result of the VTG calculations.

In FIG. 3 a flowchart illustrating some procedural steps performed whencontrolling the VTG of a vehicle in accordance with another embodimentof the present invention is shown.

Because it is desired that the exhaust gas pressure is as high aspossible during the gear shift phase and building a high exhaust gaspressure takes time, it can be advantageous to start building a highexhaust gas pressure before the actual gear shift is initiated. Such acontrol procedure is shown in FIG. 3.

Thus, first in a first step 301, the control unit calculates themaximally allowed closed position for the VTG using the current readingsfrom the pressure sensors upstream and downstream the VTG. The pressureafter the turbine can also be approximated with the outside pressure orsome other approximation.

The closed VTG position can for example be calculated using thecalculations as set out above in conjunction with FIG. 2. Thecalculations performed in step 301 are continuously renewed so that thecontrol unit at all times has access to an updated prediction value forthe closed VTG position. When a gear shift is to be performed and thepresent gear is disengaged it is desired to quickly reduce the enginespeed to a speed synchronized with the next gear after which the nextgear can be engaged. A high exhaust gas pressure will contribute toreduce the engine speed quicker and hence reduce the time necessary towait before the next gear can be engaged. Therefore it is beneficial toapply a high exhaust gas pressure just before a gear shift is to takeplace so that a high exhaust gas pressure can be generated and appliedimmediately when a gear shift begins.

Thus, when an event making it likely that a gear shift will take placein the near future occurs in a second step 303, the control unit hasaccess to data relating to the currently maximum closed VTG position andcan emit a control signal setting the VTG to the corresponding positionthereby maximizing the exhaust gas pressure in a third step 305. Inanother embodiment instead of open control of the VTG position, a closedloop control of the exhaust gas pressure can be employed. Hence, insteadof closing the VTG to the predicted position, the exhaust gas pressureis controlled to a maximum pressure that the VTG is estimated to sustainwithout suffering any damage in order to ensure that the VTG is notdamaged.

The event triggering closing of the VTG can for example be a reducedtorque demand or any other event signaling that a gear shift is likelyto occur in the near future.

Thereupon, the procedure checks if the gear shift has been completed ina fourth step 307. Also if the closing of the VTG was triggered and nogear shift was performed step 307 also times the time between thetrigger event and actual gear shift initiation. If there is no gearshift for some predetermined period of time a timer in step 307 timesout. If the gear shift has been completed or the timer in step 307 timesout, the procedure ends in a fifth step 309 and the control of the VTGis performed according to whatever control strategy the control unit isprogrammed to execute.

If, on the other hand, the gear shift has not been completed and thetimer has not timed out in step 307, the procedure continues to a sixthstep 311, where the VTG calculations as described above are updated sothat the VTG can continue to be controlled to the maximum closedposition. The procedure then returns to step 305 where the VTG is againset to a position corresponding to the result of the VTG calculations.

Furthermore, because it is likely that the power demand from the enginewill be high after completing a gear shift, keeping the exhaust gaspressure high for some time period after completion of a gear shift canbe advantageous. Thus, by keeping the VTG closed for some time aftercompleting a gear shift will maintain a high exhaust gas pressure beforethe turbine which can be used to power the turbo charger and therebyincrease the power generated by the engine immediately after a gearshift.

The methods of providing quick engine retardation in conjunction with agear shift as described herein can also be combined with a conventionalexhaust break if this turns out to be advantageous in some application.

Using the VTG to obtain a quick retardation of the engine speed isadvantageous for a number of different reasons. There is for examplelittle noise associated with building a high exhaust gas pressure. TheVTG is further relatively easy to control. In addition a high exhaustgas pressure before the turbine enables a high power to the turbocompressor.

1. A method of controlling an internal combustion engine that includes a turbo charger with a Variable Turbine Geometry for powering a motor vehicle that is provided with a gear box, the method comprising: determining an effective flow area for the Variable Turbine Geometry; determining a maximally allowed closed position for the Variable Turbine Geometry from the determined effective flow area of the Variable Turbine Geometry; detecting an event that indicates that a shifting of a gear of the motor vehicle will occur; and controlling the Variable Turbine Geometry to the maximally allowed closed position when the event is detected.
 2. The method according to claim 1, further comprising controlling exhaust gas pressure in the engine to a maximally allowed pressure value without damaging the Variable Turbine Geometry.
 3. The method according to claim 1, further comprising: storing a map of Variable Turbine Geometry positions, wherein the Variable Turbine Geometry positions have flow areas of varying effectiveness; and determining the maximally closed Variable Turbine Geometry position to be a position in the map that corresponds to a particular effective flow area.
 4. The method according to claim 1, further comprising: subsequently determining a different maximally allowed closed position for the Variable Turbine Geometry during a shifting of a gear.
 5. The method according to claim 1, wherein the event is a reduction in torque demand.
 6. A system for controlling an internal combustion engine that includes a turbo charger with a Variable Turbine Geometry for powering a motor vehicle that is provided with a gear box, the system comprising at least one control unit that is configured and operable to: determine an effective flow area for the Variable Turbine Geometry; determine a maximally allowed closed position for the Variable Turbine Geometry from the determined effective flow area of the Variable Turbine Geometry, detect an event that indicates that a shifting of a gear shift of the motor vehicle will occur; and control the Variable Turbine Geometry to the maximally allowed closed position when the event is detected.
 7. The system according to claim 6, wherein the at least one control unit is further configured and operable to control exhaust gas pressure to a maximally allowed pressure value without damaging the Variable Turbine Geometry.
 8. The system according to claim 6, wherein the at least one control unit is further configured and operable to: store a map of Variable Turbine Geometry positions, wherein the Variable Turbine Geometry positions have flow areas of varying effectiveness; and determine the maximally closed Variable Turbine Geometry position to be a position in the map that corresponds to a particular effective flow area.
 9. The system according to claim 6, wherein the at least one control unit is further configured and operable to update the maximally allowed closed position for the Variable Turbine Geometry during a shifting of a gear.
 10. The system according to claim 6, wherein the event is a reduction in torque demand.
 11. A computer readable storage medium storing a computer program product for controlling an internal combustion engine that includes a turbo charger having a Variable Geometry Turbine for powering a motor vehicle, the motor vehicle having a gear box, wherein the computer program product comprises program segments that when executed on a computer causes the computer to perform the steps of: determining an effective flow area for the Variable Turbine Geometry; determining a maximally allowed closed position for the Variable Turbine Geometry the determined effective flow area of the Variable Turbine Geometry; detecting an event that indicates that a shifting of a gear of the motor vehicle will occur; and controlling the Variable Turbine Geometry to the maximally allowed closed position when the event is detected.
 12. The computer readable storage medium storing the computer program product according to claim 11, further comprising program segments for controlling the exhaust gas pressure to a maximally allowed pressure value without damaging the Variable Turbine Geometry.
 13. The computer readable storage medium storing the computer program product according to claim 11, further comprising program segments for: storing a map of Variable Turbine Geometry positions, wherein the Variable Turbine Geometry positions have flow areas of varying effectiveness; and determining the maximally closed Variable Turbine Geometry position to be a position in the map that corresponds to the effective flow area.
 14. The computer readable storage medium storing the computer program product according to claim 11, further comprising program segments for updating the maximally allowed closed position for the Variable Turbine Geometry during a shifting of a gear.
 15. The computer readable storage medium storing the computer program product according to claim 11, wherein the event is a reduction in torque demand.
 16. (canceled)
 17. The method according to claim 4, wherein the subsequent determining of a different maximally allowed closed position for the Variable Turbine Geometry occurs repeatedly.
 18. The system according to claim 9, wherein the subsequent determining of a different maximally allowed closed position for the Variable Turbine Geometry occurs repeatedly.
 19. The computer readable storage medium storing the computer program product according to claim 14, wherein the subsequent determining of a different maximally allowed closed position for the Variable Turbine Geometry occurs repeatedly. 